1. Field of the Invention
This invention relates to an electrophotographic apparatus wherein a plurality of means in an apparatus body are constructed for movement for individual units, and more particularly to an electrophotographic apparatus wherein the distance between a photosensitive drum on a processing unit side and electrostatic image forming means is normally kept constant.
2. Description of the Prior Art
FIG. 1 is a sectional view showing a conventional electrophotographic apparatus. Referring to FIG. 1, reference numeral 1 denotes a photosensitive drum having a photoconductive layer provided on a conductive drum base body, 2 a corona discharger for charging the photosensitive drum 1, 3 an electrostatic image forming means for forming an electrostatic latent image by exposure to light, 4 a developing device, 5 a transfer corona discharger serving as a transfer device for performing transfer of a visible image obtained by development of an image, 6 a cleaning device, 7 a housing, 8 a processing unit wherein the photosensitive drum 1, corona discharger 2, developing device 4 and cleaning device 6 are supported in an integrated relationship on the housing 7, reference characters 9a and 9b denote guide rails for supporting the processing unit 8 for movement on an electrophotographic apparatus body F, reference numeral 10 denotes a rotary shaft for opening and closing the body of the electrophotographic apparatus, 11 a fixing device, 12 a discharging roller, 13 a separating roller for separating record paper from the photosensitive drum 1, 14 a register roller, 15 a pickup roller, and 16 record paper accommodated in a record paper cassette 17.
Subsequently, the operation will be described. A surface of the photosensitive drum 1 is charged uniformly with a predetermined polarity by the corona discharger 2, and then the photosensitive drum 1 is exposed to light by the electrostatic image forming means 3 to form an electrostatic latent image thereon. The electrostatic latent image formed on the drum 1 is developed into a visible image by the developing device 4. The thus formed visible image is transferred by the transfer corona discharger 5. Record paper sheets 16 accommodated in the record paper cassette 17 are forwarded one by one by rotational movement of the pickup roller 15 and transported to the transfer station by way of the register roller 14. A record paper sheet 16 to which the visible image has been transferred is separated from the photosensitive drum 1 by the separating roller 13 and then sent to the fixing device 11 at which the transferred visible image is fixed to the record paper 16. The record paper 16 is thereafter discharged by the discharging roller 12.
Since the conventional electrophotographic apparatus is constructed in such a manner as described above, the accuracy of the distance between the electrostatic image forming means 3 and the photosensitive drum 1 of the processing unit which is removable from the electrophotographic apparatus body is influenced significantly by the accuracy of parts and the accuracy in assembly, and there is a problem that the quality of a picture is deteriorated significantly particularly by eccentricity of the photosensitive drum 1. Further, in order to removably mount the photosensitive drum 1 in the form of a processing unit, it is necessary to take a sufficient distance to some degree between the electrostatic image forming means 3 and the photosensitive drum 1, and consequently, electrostatic image forming means having a long focal length (of the laser beam system or the like) is required. Thus, there is another problem that the entire electrophotographic apparatus body inevitably has a great size. It is to be noted that a technique similar to such conventional electrophotographic apparatus is disclosed in Japanese Patent Publication No. 58506/1987.